There are a number of arrangements for raw material grinding systems involving vertical roller mills. The various systems are different as regards placing of the gas conditioning tower and dedusting of the mill vent gas.
However the most common solution today is the so-called three-fan system. The three-fan system uses cyclones to dedust the mill vent gas. This arrangement reduces the operating suction and usually also the gas volume for the filter, which may be either an electrostatic precipitator or a filter of the baghouse type.
The three-fan system provides the best operational control with less interaction between operation of mill and kiln respectively. For the two-fan system, the required size of filter must be foreseen for the total mill gas flow, which is normally significantly higher than the kiln gas flow. As the mill requires significantly more gas than supplied by the kiln, a certain part of the gas flow is guided from the mill fan through the recirculation duct back to the mill.
The raw material feeding system is equipped with a magnet separator and metal detector for protection of the mill parts. In case the raw material is significantly contaminated with metal, an optional secondary refinery system can be selected.
The secondary system reduces the material to be rejected to a minimum, and at the same time the intermediate bin can be used as storage for external material during maintenance of the mill.
As a one-source supplier of complete plants, FLSmidth supplies the ATOX raw mill as well as all other equipment needed for the raw mill department.
Mill layout is based on a standardised concept and modules that ensure the most cost-effective raw mill installation.
Because gas enters the ATOX mill from one side, the ducting arrangement is as small as possible, resulting in a very compact layout. The dimensioning and selection of cyclones, mill fan and connecting ducting are optimised for low energy consumption.
The number of cyclones will be 2, 4 or 6, increasing with the mill size. The raw material feeding and recirculation system is preferably placed at the left side of the ATOX vertical mill , seen from the mill motor.
Lubrication stations for main gear, hydraulics and roller lubrication are placed with the pump station inside the structure, below the cyclones. The layout is furthermore prepared for easy access to machinery and components needing overhaul or replacement.
The mill is per default designed to be operated without enclosure, and all maintenance can be conducted by mobile crane. As grinding rollers are taken out through the main mill door, only one small area is required next to the mill for positioning of the roller after dismantling.
When required by environmental regulations, for instance noise emissions, the entire mill installation can be closed, even when not required from an operating and maintenance point of view.
When the installation is enclosed, a hoist and monorail is provided for lifting separator parts, feed sluice, mill motor and the top part of the mill gear box. The grinding mill foundation is kept at floor level, ensuring easy access around the mill.
All equipment is located at floor level or above to avoid pits and thereby ensure easy cleaning and maintenance. The material reject system includes a reject bin and subsequent metal separation and back-feeding arrangement for dust-free reject material handling.
A short belt conveyor feeding the mill and receiving the reject material ensures that the mill can start up without involving the long preceding mill feed conveyor.
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Three-fan systems most common of vertical roller mills
There are a number of arrangements for raw material grinding systems involving vertical roller mills. The various systems are different as regards placing of the gas conditioning tower and dedusting of the mill vent gas.
However the most common solution today is the so-called three-fan system. The three-fan system uses cyclones to dedust the mill vent gas. This arrangement reduces the operating suction and usually also the gas volume for the filter, which may be either an electrostatic precipitator or a filter of the baghouse type.
The three-fan system provides the best operational control with less interaction between operation of mill and kiln respectively. For the two-fan system, the required size of filter must be foreseen for the total mill gas flow, which is normally significantly higher than the kiln gas flow. As the mill requires significantly more gas than supplied by the kiln, a certain part of the gas flow is guided from the mill fan through the recirculation duct back to the mill.
The raw material feeding system is equipped with a magnet separator and metal detector for protection of the mill parts. In case the raw material is significantly contaminated with metal, an optional secondary refinery system can be selected.
The secondary system reduces the material to be rejected to a minimum, and at the same time the intermediate bin can be used as storage for external material during maintenance of the mill.
As a one-source supplier of complete plants, FLSmidth supplies the ATOX raw mill as well as all other equipment needed for the raw mill department.
Mill layout is based on a standardised concept and modules that ensure the most cost-effective raw mill installation.
Because gas enters the ATOX mill from one side, the ducting arrangement is as small as possible, resulting in a very compact layout. The dimensioning and selection of cyclones, mill fan and connecting ducting are optimised for low energy consumption.
The number of cyclones will be 2, 4 or 6, increasing with the mill size. The raw material feeding and recirculation system is preferably placed at the left side of the ATOX vertical mill , seen from the mill motor.
Lubrication stations for main gear, hydraulics and roller lubrication are placed with the pump station inside the structure, below the cyclones. The layout is furthermore prepared for easy access to machinery and components needing overhaul or replacement.
The mill is per default designed to be operated without enclosure, and all maintenance can be conducted by mobile crane. As grinding rollers are taken out through the main mill door, only one small area is required next to the mill for positioning of the roller after dismantling.
When required by environmental regulations, for instance noise emissions, the entire mill installation can be closed, even when not required from an operating and maintenance point of view.
When the installation is enclosed, a hoist and monorail is provided for lifting separator parts, feed sluice, mill motor and the top part of the mill gear box. The grinding mill foundation is kept at floor level, ensuring easy access around the mill.
All equipment is located at floor level or above to avoid pits and thereby ensure easy cleaning and maintenance. The material reject system includes a reject bin and subsequent metal separation and back-feeding arrangement for dust-free reject material handling.
A short belt conveyor feeding the mill and receiving the reject material ensures that the mill can start up without involving the long preceding mill feed conveyor.